<template>
	<view class="muqian-content" :style="{
			width,
			height
		}">
		<!-- 加载中 -->
		<view class="muqain-load u-flex u-row-center u-col-center" :style="{
					opacity:isShow?'0':'1',
					borderRadius,
					width,
					height,
					background: vk.getVuex('$app.config.bg.tab'),
					transition: `opacity ${duration/1000}s ${effect}`
					}">
			<image :src="loadSrc" class="muqian-image "  mode="widthFix" :style="{
					width: '42rpx',
					height: '42rpx'
					}"></image>
		</view>
				
		<!-- 加载成功 -->
		<image class="muqian-image" @load="load" @error="error" v-if="status==1" :src="src" :mode="mode" :style="{
				opacity:isShow?'1':'0',
				borderRadius,
				background: mode==='aspectFit'?'#000000':vk.getVuex('$app.config.bg.tab'),
				width,
				height,
				transition: `opacity ${duration/1000}s ${effect}`
				}">
		</image>
		<!-- 加载失败 -->
		
		<view class="u-flex u-row-center u-col-center" v-if="status==2" :style="{
					opacity:isShow?'1':'0',
					borderRadius,
					width,
					height,
					background: vk.getVuex('$app.config.bg.tab'),
					transition: `opacity ${duration/1000}s ${effect}`
					}">
			<image :src="errorSrc" class="muqian-image" mode="widthFix" :style="{
					width: '100rpx',
					height: '100rpx'
					}"></image>
		</view>
	</view>
</template>

<script>
	let loadTimer = null
	/**
	 * 懒加载插件
	 * @description 懒加载插件
	 *
	 * @property {String}			borderRadius		图片圆角,必须带尺寸单位
	 * @property {String}			width				图片宽度,必须带尺寸单位(默认100%)
	 * @property {String}			height				图片高度,必须带尺寸单位(默认100%)
	 * @property {String}			src					图片链接,不传的话会一直是加载中状态
	 * @property {String|Number}	minTimeOut			当图片加载过快(存在缓存)至少显示多少秒加载动画
	 * @property {String} 			effect = [linear|ease|ease-in|ease-out|ease-in-out] 过渡效果,可以用cubic-bezier
	 * 	@value linear 		规定以相同速度开始至结束的过渡效果(默认)
	 * 	@value ease  		规定慢速开始,然后变快,然后慢速结束的过渡效果
	 * 	@value ease-in 		规定以慢速开始的过渡效果
	 * 	@value ease-out		规定以慢速结束的过渡效果
	 * 	@value ease-in-out  规定以慢速开始和结束的过渡效果
	 * @property {String|Number}			duration	图片加载成功后的过渡时间,单位毫秒
	 * @property {Object}			showDistance		 当图片到屏幕哪个位置的时候开始加载,单位px,可以是负数 (默认{bottom:0})
	 * @property {String}			loadSrc				加载中显示的图片，输入网络路径或绝对路径
	 * @property {String}			errorSrc			加载失败显示的图片，输入网络路径或绝对路径
	 * @example <muqian-lazyLoad :src="src" width="100rpx" height="100rpx"></muqian-lazyLoad>
	 */

	export default {
		name: "muqian-lazyLoad",
		props: {
			//图片圆角 必须带尺寸单位
			borderRadius: {
				type: String,
				default: '12rpx'
			},
			//图片宽度
			width: {
				type: String,
				default: '100%'
			},
			height: {
				type: String,
				default: '100%'
			},
			//图片链接
			src: {
				type: String,
				default: ''
			},
			mode: {
				type: String,
				default: 'aspectFill'
			},
			//当图片加载过快(存在缓存)至少显示多少秒加载动画
			minTimeOut: {
				type: String || Number,
				default: '100'
			},
			//当图片到屏幕哪个位置的时候开始加载 单位px 可以是负数
			showDistance: {
				type: Object,
				default () {
					return {
					  left: 0,
					  right: 0,
					  top: 0,
					  bottom: 200
					}
				}
			},
			//过渡效果  linear / ease / ease-in / ease-out / ease-in-out
			effect: {
				type: String,
				default: 'linear'
			},
			//图片加载成功后的过渡时间 单位毫秒
			duration: {
				type: String || Number,
				default: '200'
			},
			//加载中图片
			loadSrc: {
				type: String,
				default: ''
			},
			//加载失败图片
			errorSrc: {
				type: String,
				default: ''
			}

		},
		data() {
			return {
				status: 0, //0加载中 1加载成功 2加载失败
				isShow: false
			}
		},
		watch: {
			//当链接变化重新加载
			src() {
				if (!this.isShow) return
				this.status = 0
				this.isShow = false
				this.$nextTick(() => {
					this.status = 1
				})
			}
		},
		mounted() {
			let intersectionObserver = uni.createIntersectionObserver(this)
			let load = false
			//当图片加载完的时候取消监听
			this.$once('destroyed', () => {
				intersectionObserver.disconnect()
			})
			intersectionObserver.relativeToViewport(this.showDistance).observe('.muqain-load', (res) => {
				if (!load && res.intersectionRatio == 0) {
					load = true
					return
				}
				load = true
				this.status = 1
				loadTimer = new Date().getTime()
				intersectionObserver.disconnect()
			})
		},
		destroyed() {
			//页面销毁取消监听
			this.$emit('destroyed')
		},
		methods: {
			load() {
				if (this.minTimeOut == 0) {
					this.isShow = true
					return
				}
				let newTimer = new Date().getTime() - loadTimer
				if (newTimer < this.minTimeOut) {
					setTimeout(() => {
						this.isShow = true
					}, this.minTimeOut - newTimer)
				} else {
					this.isShow = true
				}
			},
			error() {
				this.status = 2
				this.isShow = true
			}
		}

	}
</script>

<style lang="scss" scoped>
	.muqian-content {
		overflow: hidden;
		position: relative;

		.muqian-image {
			display: block;
		}
		.muqain-load {
			position: absolute;
			left: 0;
			top: 0;
			border-radius: 12rpx;
		}
	}
</style>
